Speaker magnet assembly

ABSTRACT

A process for manufacturing permanent magnet speaker assemblies consisting essentially only of a permanent magnet and a return path element integral with and formed from the same metallic sheet as the basket. The process comprises forming a central depression in the sheet, piercing the depression to form a central aperture, shaping the remaining depressed portion into a return path element and the remaining portion of the sheet into a basket and fitting a permanent magnet within the return path element.

United States Patent 368,821 8/1887 Edmands Inventor Rollin .1. Parker Greeuville, Mich. App! No. 798,544 Filed Dec. 16, 1968 M otSer. No. 515,322, Dec. 21,1965, Pat. No. 3,566,405. Patented Aug. 17., 1971 Assignee General Electric Company SPEAKER MAGNET ASSEMBLY 3 Claims, 13 Drawing Figs.

US. (11 29/594, 72/347 R, 72/348 R, 29/602 P, 29/607 R, 113/116 D, 1 13/120 H Int. Cl H041 7/04 Field oiSearch 179/115- -l21; 72/347, 3148;29/594, 602,607; l13/116D, 120

References Cited UNITED STATES PATENTS 2,128,614 8/1938 Kobayasbi 29/517 1,368,565 2/1921 Limont 1. 113/120 H 2,185,216 l/1940 McManusetal...... 113/1201-1 3,340,604 9/1967 Parian 29/594 FOREIGN PATENTS 1,069,684 11/1959 Germany 179/117 Primary Examiner-John F. Campbell Assistant Examiner-Robert W. Church Attorneys-Harold J. Holt, Melvin M. Goldenberg, Frank L Neuhauser and Oscar B. Waddell PATENTED AUG] v 1971 1595,32

SHEET 1 OF 2 INVENTOR RQLLIN J. PARKER BY QC A T TOPNE V PATENTED mm 7 I971 SHEET 2 [IF 2 15 FIC-ILIO FIG. I2

INVENTOR ROLLIN J. PARKER A TTOR/VEV v SPEAKER MAGNET ASSEMBLY This is a division of application Ser. No. 515,322, filed Dec. 2 l, 1965, now U.S. Pat. No. 3,466,405. This invention relates -to a speaker magnet assembly and more specifically to a process for the manufacture of a permanent magnet and basket assembly for a speaker.

Typical pennanent magnet speakers contain a basket to which are attached a permanent magnet, a pole piece and return path elements, the latter making up the yoke structure of the magnetic circuit. The return path elements in a conventional speaker will comprise one or more components which together form a cup-shaped structure surrounding the usually cylindrical speaker magnet. The return path elements must have sufficient cross-sectional area so that the flux density does not exceed the saturation point of the metal. The return path elements are therefore generally of more substantial.

gauge than the metal which makes up the speaker basket. This factor plus the shape of the path of magnetic flux in the return path circuit has resulted in the two componentsbasket and return pathbe'ing hitherto comprised of at least two separate units. Y

The present invention has as its principal object a simplified permanent magnet-basket assembly for a speaker made up of an integral return path-basket unit. It is an additional object to provide such an assembly which permits greater speaker magnet efficiency and performance. A still further object of the invention is to provide a process for manufacturing permanent magnet speaker assemblies more simply and economically than has heretofore been possible by manufacturing the speaker baskets and return path element as an integral unit.

In my copending application Ser. No. l5,40 1 now U.S. Pat. No. 3,440,364 assigned to the same assignee as the present application and filed of even date herewith, -I have dis closed a new way of orientingspeaker magnets along'a curved extent made possible by orienting the magnets as set forth in my above-identified copending application.

The speaker magnet assembly of the present invention comprises a basket having a central aperture therein, a return path element depending from said central aperture which is formed from and integral with said basket, and a permanent magnet disposed within said return path element. The magnet circuit of the speaker assembly is make up only of the permanent magnet itself and the return path element formed from the basket. No pole piece or bottom return path elements are necessary. In its preferred form, the return path element of the speaker assembly is tubular, i.e., a hollow tube open at both the bottom and the top. The speaker magnet assemblies of the invention are manufactured by shaping that portion of the basket, from which one or more of the apertures in the basket are formed, into the return path element. A permanent magnet is then fitted within the thus shaped return path element such that the magnet contacts the return path element at a lower axial extremity of the return path element and is separated from the return path element at an upward axial extremity of the return path element, the separation serving to form an airgap adapted to receive the coil ofthe speaker.

The invention will be more clearly understood from the fol lowing description taken in connection with the accompanying drawing in which FIGS. 1 through 8 illustrate schematically the successive steps of manufacture of a speaker magnet assembly of the invention; and

FIGS. 9 through 13 illustrate schematically the successive steps of manufacture of a second embodiment of a speaker magnet assembly of the invention.

In the manufacturing the speaker assemblies of the invention, a sheet 1 of relatively light-gauge, low-carbon steel is first drawn to form a central depression 2, as shown in FIG. 1. This central depression is then elongated as shown in FIG. 2. Such elongation also acts to thin out somewhat the gauge of the steel forming the depression. The depression 2 is now reverse drawn as shown in FIG. 3, to approximately double the gauge of the walls of the depression, at the same time, of course, reducing the length of the depression approximately in half. The depression 2 is now pierced as shown in FIG. 4 to form an opening 3. i

The reverse-drawn and pierced depression 2 must now be accurately sized and crimped at a die station to form the precise shape and tolerances required for optimum performance in a speaker circuit. As illustrated at FIG; 5, the depression is now shaped to form a tubular return path element 4. Specifically, tube 4 is crimped at a lower axial extremity thereof to form an annular collar 5 of reduced diameter. The inner surface of the collar 5 is flat to form continuous and close contact with the speaker magnet between the inner surface of the collar and the lower axial extremity of the magnet. The remainder of the tube is also accurately sized in order to form at 6 the precise airgap distance required upon insertion of the permanent magnet.

A typical sheet, such as l in FIG. 1, is about 0.040 inches gauge in thickness. The thickness of the reverse-drawn tube in FIG. 3 will be approximately 0.070 inches gauge, or somewhat less than twice the original gauge, the difference resulting from the elongation that has occurred in the tube.

The basket is then shaped and cut as illustrated in cross section FIGS. 6 and 7 and in plan in FIG. 8. After shaping basket 7 in conical form, four windows 8 are blanket out. A cylindrical permanent magnet 9 is press fit within integral return path element 4 as shown in FIGS. 7 and 8. Four holes 10 at each corner of the basket are also pierced to provide apertures for attachment of the speaker to a radio receiver housing or other amplification device. The complete permanent magnet circuit and basket thus consist of but two elements-the integral basket-return path element and a permanent magnet.

The process of manufacturing a speaker magnet assembly in accordance with a second embodiment of the invention is illustrated in FIGS. 9 through 13. A sheet of steel 15 is drawn as illustrated in FIG. 9 to form a depression 16 and is then pierced to form an opening 17. The pierced depression is partially reverse drawn as shown in FIG. 10 to form an annular collar 18 of reduced diameter.

The sheet 15 is now shaped and cut as illustrated in FIGS. 11 and 12 to form the conical portion of the speaker basket. This is accomplished by first shaping the sheet 15 in conical form to form the basket 19 and then piercing four holes, two of which are in the form of windows 20 and 20, as illustrated in FIG. 11. The remaining two holes 21 and 21 are pierced so as to leave T-shaped tabs 22 and 22' integral with the basket. Each of the T-shaped tabs is then bent downward and away from the basket and shaped into the form of a half of a hollow cylinder or tube, as illustrated in FIG. 12. Upon further bending down and back, tabs 22 and 22' form intimate contact with depression 16. The tabs 22 and 22 and depression 16 now together form double-gauge walls of the completed return path element 23, as illustrated in FIG. 13. After accurately sizing the return path element, a permanent magnet may be press fit within the shaped return path element to form the speaker magnet assembly as shown in connection with the first embodirnent.

The invention is, to a considerable extent, made possible by the utilization of a permanent magnet oriented in a manner set forth in my above-referred-to copending application Ser. No. 515,401, now U.S. Pat. No. 3,440,364. As there set forth, the permanent magnet is oriented along an axially disposed curve. Such orientation is shown at 11 in FIG. 7 of the drawing of the present application. This permits a number of significant advantages in the construction of the permanent magnet speaker. Measurements indicate that percent of the total magnetomotive force is made available at the airgap as opposed to 6575 percent in conventional magnet structures. Additionally, virtually I00 percent of the total magnetic flux may be made to enter the general region of the voice coil vs. a loss of as much as percent of such flux to regions outside the voice coil regions in conventional magnet structures. Because of the greater efficiency of the magnetic circuit, it is possible to use lower flux densities to achieve equivalent airgap densities and thus equivalent speaker performance. This permits a smaller cross-sectional area in the return path ele ment because the flux density per unit of return path is smaller. This enables efficient speaker magnet structures to be built, utilizing thin-gauge, soft-steel return paths, thus enabling the return path element itself to be made of the same material as the basket. This, in effect, permits utilization as a return path element of a portion of the basket structure previousiy discarded. Additionally, because of the manner in which the permanent magnet is oriented, a conventional bottom return path element is unnecessary.

Another advantage of the invention is also illustrated in FIG. 7. The width of the airgap 12 is the same as the width of the throat 13 formed between the remainder of the return path element and the lateral sides of the permanent magnet. While this structure is not unknown in the speaker art, it has almost always been avoided because greatest efficiency in speaker structures is obtained by maintaining a large degree of separation between the axial flow of magnetic flux in the magnet and the return axial flow in the lateral portion of the return path. This discourages radiation of flux from the sides of the magnet to the return path element at areas other than the airgap. In conventional speaker assemblies the flux flows in an axial direction through the permanent magnetany radial flow of flux other than at the extremities of the magnet must be discouraged. In the speaker magnet construction shown in FIG. 7, there is already a radial component (toward the sides of the magnet) in the flow of flux in the magnet so that radial flow is not discouraged except for a very small area at the axial center of the magnet. The invention thus makes it possible to reduce considerably the dimensions of the throat area of the permanent magnet return path system and thus to miniaturize the construction of the speaker. While the airgap l2 and throat 13 need not be the same dimension as in H6. 7, the

throat section may nevertheless be narrower in the present speakers than in conventional speaker structures.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A process for manufacturing a permanent magnet assembly for a speaker from a single metallic sheet comprising forming a central depression in said sheet,

removing the central portion of said depression in order to form a central aperture in said sheet, at least partially doubling back the remaining portion of the depression and reducing the diameter of the lower extremity of the doubled-back portion to form a return path element having a lower extremity of reduced diameter shaping the remaining portion of the sheet into a basket integral with and formed from the same sheet as the return path element,

fitting a permanent magnet within said return path element and forming continuous and close contact between the lower extremity of the magnet and the reduced diameter of the return path element to form a permanent magnet assembly.

2. The process of claim 1 in which the return path element is coaxial with said central aperture.

3. A process for manufacturing a generally conically shaped permanent magnet assembly for a speaker from a single metallic sheet comprising forming a cuplike central depression in said sheet,

removing the central portion of the said depression in order to form a central aperture in said sheet,

incompletely cutting two noncentrally located apertures radially spaced from said central depression and shaping the metal from which said apertures are cut into a return path element coaxial with said central aperture, shaping the remaining portion of the sheet into a basket integral with and formed from the same sheet as the return path element,

fitting a permanent magnet within said return path element to form a permanent magnet assembly. 

1. A process for manufacturing a permanent magnet assembly for a speaker from a single metallic sheet comprising forming a central depression in said sheet, removing the central portion of said depression in order to form a central aperture in said sheet, at least partially doubling back the remaining portion of the depression and reducing the diameter of the lower extremity of the doubled-back portion to form a return path element having a lower extremity of reduced diameter shaping the remaining portion of the sheet into a basket integral with and formed from the same sheet as the return path element, fitting a permanent magnet within said return path element and forming continuous and close contact between the lower extremity of the magnet and the reduced diameter of the return path element to form a permanent magnet assembly.
 2. The process of claim 1 in which the return path element is coaxial with said central aperture.
 3. A process for manufacturing a generally conically shaped permanent magnet assembly for a speaker from a single metallic sheet comprising forming a cuplike central depression in said sheet, removing the central portion of the said depression in order to form a central aperture in said sheet, incompletely cutting two noncentrally located apertures radially spaced from said central depression and shaping the metal from which said apertures are cut into a return path element coaxial with said central aperture, shaping the remaining portion of the sheet into a basket integral with and formed from the same sheet as the return path element, fitting a permanent magnet within said return path element to form a permanent magnet assembly. 